There are a large number of serious non-malignant diseases of childhood, most of them congenital and rare, which can be corrected by HSCT. These diseases are all characterized by deficiencies, either in number or in function, of marrow derived cells. These diseases usually affect immune or blood cells and frequently involve transfusion therapy with erythrocytes, platelets or granulocytes. Examples of such diseases include sickle cell disease, thalassemia major, Glanzmann thrombasthenia, Wiskott-Aldrich syndrome, chronic-granulomatous disease, severe congenital neutropenia, leukocyte adhesion deficiency, Shwachman-Diamond syndrome, Diamond-Blackfan anemia, Fanconi anemia, dyskeratosis-congenita, Chediak-Higashi syndrome, and severe aplastic anemia.